A benzopyran compound which is useful for an antiarrhythmic drug and a process for producing the same have been disclosed. That is, a benzopyran compound is produced by asymmetric epoxidation of chromene compound using an optically active manganese complex to obtain an optically active chromene oxide compound and then ring-opening the epoxide with an amine compound (see Patent Document 1).
A process for producing an optically active chromene oxide compound by asymmetric epoxidation of chromene compound using an optically active manganese complex has already been disclosed (see Patent Document 2, Patent Document 3, Patent Document 4, Patent Document 5 and Patent Document 6). In the above-described patent documents, production examples of optically active chromene oxide compounds using optically active manganese complexes as catalysts and iodosobenzene, sodium hypochlorite or 30% hydrogen peroxide aqueous solution as co-oxidizing reagent have been described.
For an asymmetric oxidation reaction using an optically active manganese complex, an additive called for an axial ligand such as 4-phenylpyridine-N-oxide is needed other than a co-oxidizing reagent, so that a different process for producing an optically active chromene oxide without using an axial donor ligand has been desired.
In contrast, it has been described that even 0.01 to 0.2 mol % use of an asymmetric optically active manganese complex can produce an optically active chromene oxide compound in high chemical yield and optical yield (see Patent Document 7). However, only the example of iodosobenzene used as co-oxidizing reagent is described in this patent document. Accordingly, more advantageous and efficient process for producing has been desired.
In an optically active titanium complex, it has been reported that use of a di-μ-oxotitanium-salalen complex provides a highly enantioselective reaction in the asymmetric epoxidation of various simple olefins not having heteroatom(s). However, there were no examples of olefinic compounds having heteroatom(s) and chromene compounds in the report (Non-patent Document 8).    [Patent Document 1] Japanese Patent Application Publication No. JP-A-2001-151767    [Patent Document 2] Japanese Patent Application Publication No. JP-A-05-301878    [Patent Document 3] Japanese Patent Application Publication No. JP-A-07-285983    [Patent Document 4] Japanese Patent Application Publication No. JP-A-08-245668    [Patent Document 5] WO 2005/090357A1    [Patent Document 6] WO 2005/080368A2    [Patent Document 7] Japanese Patent Application Publication No. JP-A-11-335384    [Non-patent Document 8] K. Matsumoto, Y. Sawada, B. Saito, K. Sakai and T. Katsuki, Angew. Chem. Int. Ed. (2005), 44, 4935-4939.